我有这张表：
+------------+-----------+--------+-------+------------+
| username | exam_code | module | value | percentage |
+------------+-----------+--------+-------+------------+
| aaaaa | x | 1 | 60 | - |
| aaaaa | x | 2 | 80 | - |
| aaaaa | x | 3 | 70 | - |
| bbbbb | x | 1 | 60 | - |
| bbbbb | x | 2 | 70 | - |
| bbbbb | x | 3 | 90 | - |
+------------+-----------+--------+-------+------------+
我想输入自己（使用php POST），模块的百分比
例如，如果我提出module 1 = 50%，module 2 = 35%，module 3 = 15%
（总数将是100）
它会将上一个表格变为：
+------------+-----------+--------+-------+------------+
| username | exam_code | module | value | percentage |
+------------+-----------+--------+-------+------------+
| aaaaa | x | 1 | 60 | 50 |
| aaaaa | x | 2 | 80 | 35 |
| aaaaa | x | 3 | 70 | 15 |
| bbbbb | x | 1 | 70 | 50 |
| bbbbb | x | 2 | 70 | 35 |
| bbbbb | x | 3 | 90 | 15 |
+------------+-----------+--------+-------+------------+
直到这一行，我可以用PHP
来做到这一点我想问的是，如何将此表（在输入的百分比字段之后）转换为此
+------------+----------+----------+----------+
| username | module 1 | module 2 | module 3 |
+------------+----------+----------+----------+
| aaaaa | 30 | 28 | 10.5 |
| bbbbb | 35 | 24.5 | 13.5 |
+------------+----------+----------+----------+
（解释）
+------------+----------+----------+----------+
| username | module 1 | module 2 | module 3 |
+------------+----------+----------+----------+
| aaaaa | (60x50%) | (80x35%) | (70x15%) |
| bbbbb | (70x50%) | (70x35%) | (90x15%) |
+------------+----------+----------+----------+
如何SELECT（不创建表）来获取此表，只使用MySQL语法？
答案 0 :(得分：4)
这样的事情应该这样做。
SELECT username,
SUM(CASE WHEN module = 1 THEN value*percentage/100 END) as module1,
SUM(CASE WHEN module = 2 THEN value*percentage/100 END) as module2,
SUM(CASE WHEN module = 3 THEN value*percentage/100 END) as module3
FROM tablename
GROUP BY username